Charge and discharge control circuit and battery device

ABSTRACT

A short-circuit and overcurrent detecting circuit includes a reference voltage circuit including a constant current circuit, a first impedance element, a first transistor having a resistance value depending a voltage of a secondary battery, a second impedance element, and a second transistor having a resistance value depending the voltage of the secondary battery, which are connected in series. The reference voltage circuit outputs a first reference voltage from a node of the constant current circuit and the first impedance element, and outputs a second reference voltage from a node of the first transistor and the second impedance element. The short-circuit and overcurrent detecting circuit further includes: a first comparator circuit for comparing a voltage of an overcurrent detecting terminal with the first reference voltage; and a second comparator circuit for comparing the voltage of the overcurrent detecting terminal with the second reference voltage.

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119 to Japanese PatentApplication No. 2014-100195 filed on May 14, 2014, the entire contentsof which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a battery device including a secondarybattery and a charge and discharge control circuit configured to detecta voltage and abnormality of the secondary battery to control charge anddischarge of the secondary battery, and more particularly, to a chargeand discharge control circuit and a battery device that are capable ofpreventing a battery from entering an abnormal state or preventing anexcessive current from flowing through a battery or an apparatusconnected to the battery.

2. Description of the Related Art

FIG. 4 is a circuit diagram illustrating a related-art battery deviceincluding a charge and discharge control circuit. The related-artbattery device including the charge and discharge control circuitincludes a secondary battery 11, an N-channel discharge control fieldeffect transistor 12, an N-channel charge control field effecttransistor 13, a charge and discharge control circuit 14, resistors 22and 31, a capacitor 32, and external terminals 20 and 21. The charge anddischarge control circuit 14 includes a control circuit 15, anovercurrent detecting circuit 530, a short-circuit detecting circuit540, an overcurrent detecting terminal 19, a charge control signaloutput terminal 41, a discharge control signal output terminal 42, a DSterminal 45, a positive electrode power supply terminal 44, and anegative electrode power supply terminal 43. The overcurrent detectingcircuit 530 includes a comparator circuit 101 and a reference voltagecircuit 531. The short-circuit detecting circuit 540 includes acomparator circuit 102 and a reference voltage circuit 541.

The control circuit 15 includes resistors 504, 505, 506, 507, 518, and528, reference voltage circuits 509 and 515, comparator circuits 501,508, and 513, an oscillator circuit 502, a counter circuit 503, a logiccircuit 510, a level shift circuit 511, a delay circuit 512, a logiccircuit 520, and NMOS transistors 517 and 519.

Next, an operation of the related-art battery device including thecharge and discharge control circuit is described. When a load isconnected between the external terminals 20 and 21 and a current flows,a potential difference is generated between a negative electrode of thesecondary battery 11 and the external terminal 21. This potentialdifference is determined based on a current amount I₁ flowing betweenthe external terminals 20 and 21, a resistance value R₁₂ of theN-channel discharge control field effect transistor 12, and a resistancevalue R₁₃ of the N-channel charge control field effect transistor 13,and is represented by I₁×(R₁₂+R₁₃). A voltage of the overcurrentdetecting terminal 19 is equal to a voltage of the external terminal 21.The comparator circuit 101 compares a voltage of the reference voltagecircuit 531 with the voltage of the overcurrent detecting terminal 19.When the voltage of the overcurrent detecting terminal 19 is higher, theN-channel discharge control field effect transistor 12 is turned off forovercurrent protection. A setting value of an overcurrent detectioncurrent value is represented by I_(DOP), a voltage of the referencevoltage circuit 531 is represented by V₅₃₁, a resistance value of theN-channel discharge control field effect transistor 12 is represented byR₁₂, and a resistance value of the N-channel charge control field effecttransistor 13 is represented by R₁₃. A voltage of the external terminal21 as a threshold voltage for the comparator circuit 101 to output adetection signal is V₅₃₁. At this time, the current flowing between theexternal terminals 20 and 21 is obtained by dividing the voltage of theexternal terminal 21 by the sum of the resistance values of theN-channel discharge control field effect transistor 12 and the N-channelcharge control field effect transistor 13, and is represented byI_(DOP)=V₅₃₁/(R₁₂+R₁₃).

A voltage of the overcurrent detecting terminal of the charge anddischarge control circuit as a threshold voltage for the comparatorcircuit 101 to output a detection signal is referred to as “overcurrentdetection voltage”. A voltage of the overcurrent detecting terminal ofthe charge and discharge control circuit as a threshold voltage for thecomparator circuit 102 to output a detection signal is referred to as“short-circuit detection voltage”.

However, in the related art, the overcurrent detection voltage and theshort-circuit detection voltage of the charge and discharge controlcircuit have constant values even when the secondary battery voltage ortemperature changes, but the resistance value of the N-channel chargeand discharge control field effect transistor changes along with achange in the secondary battery voltage or temperature, resulting influctuations in an overcurrent detection current value and ashort-circuit detection current value. Accordingly, there is a problemin that the overcurrent detection current value and the short-circuitdetection current value are low in accuracy to reduce the safety of thebattery device. Further, there is another problem in that currentconsumption is high because two reference voltage circuits are used forthe overcurrent detecting circuit and the short-circuit detectingcircuit.

SUMMARY OF THE INVENTION

The present invention has been made to solve the above-mentionedproblems, and aims at changing an overcurrent detection voltage and ashort-circuit detection voltage of a charge and discharge controlcircuit so as to follow a change in a resistance value of an N-channelcharge and discharge control field effect transistor caused by a changein a secondary battery voltage or temperature, to thereby prevent anovercurrent detection current value from being fluctuated by the changein the secondary battery voltage or temperature. Accordingly, thepresent invention provides a highly safe battery device in which theaccuracy of the overcurrent detection current value and a short-circuitdetection current value is improved with low current consumption.

In order to solve the related-art problems, a charge and dischargecontrol circuit according to one embodiment of the present invention hasthe following configuration.

A short-circuit and overcurrent detecting circuit includes: a referencevoltage circuit including a constant current circuit, a first impedanceelement, a first transistor having a resistance value that is changeddepending on a voltage of a secondary battery, a second impedanceelement, and a second transistor having a resistance value that ischanged depending on the voltage of the secondary battery, which areconnected in series, the reference voltage circuit being configured tooutput a first reference voltage from a node of the constant currentcircuit and the first impedance element, and output a second referencevoltage from a node of the first transistor and the second impedanceelement; a first comparator circuit configured to compare a voltage ofan overcurrent detecting terminal with the first reference voltage; anda second comparator circuit configured to compare the voltage of theovercurrent detecting terminal with the second reference voltage.

According to the one embodiment of the present invention, a secondarybattery voltage dependence and a temperature dependence of anovercurrent detection voltage and a short-circuit detection voltage ofthe charge and discharge control circuit may be matched with a secondarybattery voltage dependence and a temperature dependence of a resistancevalue of a charge and discharge control switch, and hence even when thesecondary battery voltage or temperature changes, an overcurrentdetection current value and a short-circuit detection current value ofthe battery device are constant. Consequently, a highly safe batterydevice in which the accuracy of the overcurrent detection current valueand the short-circuit detection current value is improved with lowcurrent consumption may be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of a charge and discharge control circuitand a battery device according to a first embodiment of the presentinvention.

FIG. 2 is a circuit diagram of a charge and discharge control circuitand a battery device according to a second embodiment of the presentinvention.

FIG. 3 is a circuit diagram of a charge and discharge control circuitand a battery device according to a third embodiment of the presentinvention.

FIG. 4 is a circuit diagram of a charge and discharge control circuitand a battery device according to the related art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

FIG. 1 is a circuit diagram of a charge and discharge control circuitand a battery device according to a first embodiment of the presentinvention.

The charge and discharge control circuit and the battery device of thefirst embodiment include a secondary battery 11, an N-channel dischargecontrol field effect transistor 12, an N-channel charge control fieldeffect transistor 13, a charge and discharge control circuit 14,resistors 22 and 31, a capacitor 32, and external terminals 20 and 21.The charge and discharge control circuit 14 includes a control circuit15, a short-circuit and overcurrent detecting circuit 110, anovercurrent detecting terminal 19, a charge control signal outputterminal 41, a discharge control signal output terminal 42, a positiveelectrode power supply terminal 44, and a negative electrode powersupply terminal 43. The short-circuit and overcurrent detecting circuit110 includes comparator circuits 101 and 102, a constant current circuit103, resistors 104 and 106, and NMOS transistors 105 and 107. Theconstant current circuit 103, the resistors 104 and 106, and the NMOStransistors 105 and 107 form a reference voltage circuit.

The secondary battery 11 has a positive electrode connected to theexternal terminal 20 and the resistor 31, and a negative electrodeconnected to the capacitor 32, the negative electrode power supplyterminal 43, and a source and a back gate of the N-channel dischargecontrol field effect transistor 12. The positive electrode power supplyterminal 44 is connected to a node of the resistor 31 and the capacitor32. The N-channel discharge control field effect transistor 12 has agate connected to the discharge control signal output terminal 42, and adrain connected to a drain of the N-channel charge control field effecttransistor 13. The N-channel charge control field effect transistor 13has a gate connected to the charge control signal output terminal 41,and a source and a back gate connected to the external terminal 21 andone terminal of the resistor 22. The other terminal of the resistor 22is connected to the overcurrent detecting terminal 19.

The comparator circuit 101 has an inverting input terminal connected tothe overcurrent detecting terminal 19, a non-inverting input terminalconnected to a node of one terminal of the constant current circuit 103and one terminal of the resistor 104, and an output terminal connectedto the control circuit 15. The other terminal of the constant currentcircuit 103 is connected to the positive electrode power supply terminal44. The NMOS transistor 105 has a gate connected to the positiveelectrode power supply terminal 44, a drain connected to the otherterminal of the resistor 104, and a source connected to one terminal ofthe resistor 106. The NMOS transistor 107 has a gate connected to thepositive electrode power supply terminal 44, a drain connected to theother terminal of the resistor 106, and a source connected to thenegative electrode power supply terminal 43. The comparator circuit 102has an inverting input terminal connected to the overcurrent detectingterminal 19, a non-inverting input terminal connected to the source ofthe NMOS transistor 105, and an output terminal connected to the controlcircuit 15. The control circuit 15 has a power supply terminal connectedto the positive electrode power supply terminal 44, a ground terminalconnected to the negative electrode power supply terminal 43, a firstoutput terminal connected to the discharge control signal outputterminal 42, and a second output terminal connected to the chargecontrol signal output terminal 41.

Next, an operation of the charge and discharge control circuit and thebattery device of this embodiment is described. When the voltage of thesecondary battery 11 is equal to or lower than an overcharge detectionvoltage and equal to or higher than an overdischarge detection voltage,the N-channel discharge control field effect transistor 12 and theN-channel charge control field effect transistor 13 are controlled to beturned on. When a load is connected between the external terminals 20and 21 in this state and a discharge current is caused to flow, apotential difference is generated between the negative electrode of thesecondary battery 11 and the external terminal 21. This potentialdifference is determined based on a current amount I1 flowing betweenthe external terminals 20 and 21, a resistance value R₁₂ of theN-channel discharge control field effect transistor 12, and a resistancevalue R₁₃ of the N-channel charge control field effect transistor 13,and is represented by I₁×(R₁₂+R₁₃).

The constant current circuit 103 causes a current to flow through theresistors 104 and 106 and the NMOS transistors 105 and 107 to generate avoltage, and outputs the voltage as a reference voltage of the referencevoltage circuit. The comparator circuit 102 compares the referencevoltage of the reference voltage circuit with a voltage of theovercurrent detecting terminal 19. When the voltage of the overcurrentdetecting terminal 19 is higher, the comparator circuit 102 outputs adetection signal to the control circuit 15 to turn off the N-channeldischarge control field effect transistor 12 for overcurrent protection.

A setting value of an overcurrent detection current value is representedby I_(DOP), a voltage generated at a node of the source of the NMOStransistor 105 and the resistor 106 of the reference voltage circuit isrepresented by V_(ref), a resistance value of the N-channel dischargecontrol field effect transistor 12 is represented by R₁₂, and aresistance value of the N-channel charge control field effect transistor13 is represented by R₁₃. A voltage of the external terminal 21 as athreshold voltage for the comparator circuit 102 to output a detectionsignal is V_(ref). At this time, the current flowing between theexternal terminals 20 and 21 is obtained by dividing the voltage of theexternal terminal 21 by the sum of the resistance values of theN-channel discharge control field effect transistor 12 and the N-channelcharge control field effect transistor 13, and is represented byI_(DOP)=V_(ref)/(R₁₂+R₁₃).

In this case, the resistance value of the N-channel field effecttransistors has a gate-source voltage dependence and a temperaturedependence. A source potential of the N-channel charge and dischargecontrol field effect transistors is a negative electrode potential ofthe secondary battery, and a gate potential thereof is a positiveelectrode potential of the secondary battery. Accordingly, theresistance value (R₁₂+R₁₃) of the N-channel charge and discharge controlfield effect transistors has a secondary battery voltage dependence anda temperature dependence.

The source of the NMOS transistor 107 is connected to the negativeelectrode power supply terminal 43 and the gate thereof is connected tothe positive electrode power supply terminal 44, and hence the NMOStransistor 107 creates the state in which a gate-source voltage thereofis the same as that of the N-channel charge and discharge control fieldeffect transistors.

When a length W and a length L of the NMOS transistor 107 are changedand an amount of current flowing into the NMOS transistor 107 is changedby the constant current circuit 103, a secondary battery voltagedependence of V_(ref) can be adjusted. Further, in order to adjust theovercurrent detection current value T_(DOP), which is represented byV_(ref)/(R₁₂+R₁₃), the absolute value of V_(ref) needs to be calibrated.Through optimization of the value of the resistor 106 based on thecurrent value of the constant current circuit 103 so that V_(ref) isI_(DOP)×(R₁₂+R₁₃), a target value of the overcurrent detection currentis adjusted. Further, temperature characteristics of the resistor 106can be adjusted by changing the method of manufacturing an element. Whenthe absolute value of V_(ref) is calibrated, the temperaturecharacteristics of the resistor 106 need to be optimized so thattemperature characteristics of V_(ref) match with temperaturecharacteristics of the N-channel charge and discharge control fieldeffect transistors.

A setting value of a short-circuit detection current value isrepresented by I_(SHORT), and a voltage generated at a node of theconstant current circuit 103 and the resistor 104 of the referencevoltage circuit is represented by V_(ref2). A voltage of the externalterminal 21 as a threshold voltage for the comparator circuit 101 tooutput a detection signal is V_(ref2). At this time, the current flowingbetween the external terminals 20 and 21 is obtained by dividing thevoltage of the external terminal 21 by the sum of the resistance valuesof the N-channel discharge control field effect transistor 12 and theN-channel charge control field effect transistor 13, and is representedby I_(SHORT)=V_(ref2)/(R₁₂+R₁₃).

Further, a potential difference VΔ generated between the resistor 104and the NMOS transistor 105 is represented byVΔ=V_(ref2)−V_(ref)=(I_(SHORT)−I_(DOP))×(R₁₂+R₁₃).

In this case, the resistance value of the N-channel field effecttransistors has a gate-source voltage dependence and a temperaturedependence. A source potential of the N-channel charge and dischargecontrol field effect transistors is a negative electrode potential ofthe secondary battery, and a gate potential thereof is a positiveelectrode potential of the secondary battery. Accordingly, theresistance value (R₁₂+R₁₃) of the N-channel charge and discharge controlfield effect transistors has a secondary battery voltage dependence anda temperature dependence. The source of the NMOS transistor 105 isconnected to the resistor 106 and the gate thereof is connected to thepositive electrode power supply terminal 44, and hence the NMOStransistor 105 creates the state in which a gate-source voltage thereofis the same as that of the N-channel charge and discharge control fieldeffect transistors.

When a length W and a length L of the NMOS transistor 105 are changedand an amount of current flowing into the NMOS transistor 105 is changedby the constant current circuit 103, a secondary battery voltagedependence of VΔ can be adjusted. Further, in order to adjust theshort-circuit detection current value I_(SHORT), which is represented byVΔ/(R₁₂+R₁₃)+I_(DOP), the absolute value of VΔ needs to be calibrated.Through optimization of the value of the resistor 104 based on thecurrent value of the constant current circuit 103 so that VΔ is(I_(SHORT)−I_(DOP))×(R₁₂+R₁₃), a target value of the short-circuitdetection current is adjusted. Further, temperature characteristics ofthe resistor 104 can be adjusted by changing the method of manufacturingan element. When the absolute value of VΔ is calibrated, the temperaturecharacteristics of the resistor 104 need to be optimized so thattemperature characteristics of VΔ match with temperature characteristicsof the N-channel charge and discharge control field effect transistors.

In this manner, the secondary battery voltage dependence and thetemperature dependence of the value of the reference voltage of thereference voltage circuit can be adjusted so as to match with thesecondary battery voltage dependence and the temperature dependence ofthe resistance value of the N-channel charge and discharge control fieldeffect transistors. Consequently, the setting value I_(DOP) of theovercurrent detection current value and the setting value I_(SHORT) ofthe short-circuit detection current value can be maintained constanteven when the secondary battery voltage or temperature changes. Further,the detection can be performed even without using a reference voltagecircuit for short-circuit detection, and hence current consumption canbe reduced.

Note that, the gates of the NMOS transistor 105 and the NMOS transistor107 are connected to the positive electrode power supply terminal 42 ofthe charge and discharge control circuit 14, but the resistance value ofthe N-channel charge and discharge control field effect transistors onlyneeds to be changed in response to detection of the secondary batteryvoltage, and hence the same effect as in the first embodiment can beexerted as long as the gates of the NMOS transistor 105 and the NMOStransistor 107 are connected to a circuit having a secondary batteryvoltage dependence and the constant current value is adjusted. Further,the N-channel discharge control field effect transistor 12, theN-channel charge control field effect transistor 13, and the NMOStransistor 105 are used in the description, but the present invention isnot limited to this configuration. It is needless to say that, even whenP-channel field effect transistors are used, the NMOS transistor 105 ischanged to a PMOS transistor, and the constant current circuit 103 isconnected to the negative electrode power supply terminal 43 instead ofthe positive electrode power supply terminal 44, a similar operation isenabled. Further, the resistor 104 and the resistor 106 are not limitedto the configuration described above, and any impedance element may beused as long as the element has impedance.

As described above, the battery device of the first embodiment can matchthe secondary battery voltage dependence and the temperature dependenceof the overcurrent detection voltage and the short-circuit detectionvoltage of the charge and discharge control circuit with the secondarybattery voltage dependence and the temperature dependence of theN-channel charge and discharge control field effect transistors, tothereby improve the accuracy of the overcurrent detection current valueand the short-circuit detection current value of the battery device andenhance the safety of the battery device. Further, current consumptioncan be reduced because a reference voltage circuit for short-circuitdetection is not used.

Second Embodiment

FIG. 2 is a circuit diagram of a charge and discharge control circuitand a battery device according to a second embodiment of the presentinvention. The second embodiment differs from the first embodiment inthat the resistors 104 and 106 are changed to NMOS transistors 201 and202.

The NMOS transistor 201 has a gate connected to the positive electrodepower supply terminal 44, a drain connected to the non-inverting inputterminal of the comparator circuit 101, and a source connected to thedrain of the NMOS transistor 105. The NMOS transistor 202 has a gateconnected to the positive electrode power supply terminal 44, a drainconnected to the non-inverting input terminal of the comparator circuit102, and a source connected to the drain of the NMOS transistor 107. Theremaining connection is similar to that in the first embodiment. Evenwith such a configuration, the setting value of the overcurrentdetection current value and the setting value of the short-circuitdetection current value can be maintained constant even when thesecondary battery voltage or temperature changes.

Note that, in the case where the temperature characteristics areadjusted by the NMOS transistors 201 and 202, the method ofmanufacturing an element may be changed to adjust the temperaturecharacteristics, such as the use of dual-gate transistors.

As described above, the battery device of the second embodiment canmatch the secondary battery voltage dependence and the temperaturedependence of the overcurrent detection voltage and the short-circuitdetection voltage of the charge and discharge control circuit with thesecondary battery voltage dependence and the temperature dependence ofthe N-channel charge and discharge control field effect transistors, tothereby improve the accuracy of the overcurrent detection current valueand the short-circuit detection current value of the battery device andenhance the safety of the battery device. Further, current consumptioncan be reduced because a reference voltage circuit for short-circuitdetection is not used.

Third Embodiment

FIG. 3 is a circuit diagram of a charge and discharge control circuitand a battery device according to a third embodiment of the presentinvention. The third embodiment differs from the battery device of thefirst embodiment in that a resistor 301 is added between a node of thenegative electrode of the secondary battery 11 and the negativeelectrode power supply terminal 43 and the source of the N-channeldischarge control field effect transistor 12. All the remainingconnection is similar to that in the first embodiment.

An on-resistance R₁₂ of the N-channel discharge control field effecttransistor 12 and an on-resistance R₁₃ of the N-channel charge controlfield effect transistor 13 greatly fluctuate in the manufacturingprocess and are low in accuracy. To deal with this, a resistor 33, whichhas less fluctuations in resistance value than the N-channel fieldeffect transistors, is connected in series to the N-channel field effecttransistors. In this manner, the fluctuations in overcurrent detectioncurrent value can be reduced. The operations of detecting theovercurrent and the short-circuit current are the same as in the firstembodiment, and can be realized also by the configuration of FIG. 3.

Note that, the position of the resistor 301 is not limited to theposition of FIG. 3, and the resistor 301 may be connected at anyposition between the node of the negative electrode of the secondarybattery 11 and the negative electrode power supply terminal 43 and anode of the external terminal 21 and the resistor 22. Further, theresistor 301 may not be a resistor formed by design, and may be aparasitic resistor formed when the circuit is constructed. Further, theconfiguration of the third embodiment may be used not only for theconfiguration of the first embodiment but also for the configuration ofthe second embodiment.

As described above, the battery device of the third embodiment can matchthe secondary battery voltage dependence and the temperature dependenceof the overcurrent detection voltage and the short-circuit detectionvoltage of the charge and discharge control circuit with the secondarybattery voltage dependence and the temperature dependence of theN-channel charge and discharge control field effect transistors, tothereby improve the accuracy of the overcurrent detection current valueand the short-circuit detection current value of the battery device andenhance the safety of the battery device. Further, current consumptioncan be reduced because a reference voltage circuit for short-circuitdetection is not used.

What is claimed is:
 1. A charge and discharge control circuit,comprising: a control circuit configured to detect a voltage andabnormality of a secondary battery; and a short-circuit and overcurrentdetecting circuit configured to detect an overcurrent and a shortcircuit based on a voltage of an overcurrent detecting terminal, theshort-circuit and overcurrent detecting circuit comprising: a referencevoltage circuit comprising a constant current circuit, a first impedanceelement connected to the constant current circuit, a first transistorincluding a drain connected to the first impedance element, and having aresistance value that is changed depending on the voltage of thesecondary battery, a second impedance element connected to a source ofthe first transistor, and a second transistor including a drainconnected to the second impedance element, and having a resistance valuethat is changed depending on the voltage of the secondary battery, thereference voltage circuit being configured to output a first referencevoltage from a node of the constant current circuit and the firstimpedance element, and output a second reference voltage from a node ofthe first transistor and the second impedance element; a firstcomparator circuit configured to compare the voltage of the overcurrentdetecting terminal with the first reference voltage; and a secondcomparator circuit configured to compare the voltage of the overcurrentdetecting terminal with the second reference voltage.
 2. A charge anddischarge control circuit according to claim 1, wherein the firstimpedance element comprises a third transistor having a resistance valuethat is changed depending on the voltage of the secondary battery, andwherein the second impedance element comprises a fourth transistorhaving a resistance value that is changed depending on the voltage ofthe secondary battery.
 3. A battery device, comprising: a secondarybattery; a charge and discharge control switch connected in a charge anddischarge path of the secondary battery; and the charge and dischargecontrol circuit according to claim 1 configured to monitor a voltage ofthe secondary battery to control the charge and discharge controlswitch.
 4. A battery device according to claim 3, further comprising aresistor connected in the charge and discharge path between thesecondary battery and an external terminal, in which the charge anddischarge control switch is connected.